This invention relates generally to a brake wear indicator and more particularly to a device providing visible indication of excessive wear of a friction material in a friction coupling.
Friction couplings in the form of vehicle brakes and clutches are widely used in construction machinery to facilitate the stop and go movement of such machinery. The friction couplings used in construction machinery typically have one or more friction discs which rotate within a brake housing between a brake piston and a reaction member. The number of friction discs used depends on the braking requirement of the machine in which the friction coupling is used. In the instance where multiple friction discs are used, reaction discs splined to the brake housing are interleaved between the friction discs splined to a rotating member. The rotating friction discs typically have friction material bonded to each side thereof. When braking of the rotating member is desired, the brake piston is actuated, by fluid pressure, to move the piston axially against the adjacent reaction disc thereby capturing the friction discs between the reaction discs and a reaction surface on the brake housing.
Friction braking creates heat and friction which results in a primary wear of the friction material on the friction discs and a secondary wear of the reaction discs. To prevent unscheduled machinery down time, the friction discs need to be replaced before they wear to a point where they are incapable of performing the braking function, namely, before all the friction material has been worn away from the friction discs.
Various devices have heretofore been employed to determine brake wear. U.S. Pat. No. 5,697,472 issued Dec. 16, 1997 to Gordon L. Walker et. al. for a Wear Indicator discloses a brake wear indicating apparatus which includes a brake wear monitoring pin supported in a bore of a brake housing and positioned for end abutment with, and axial movement by, a power operated brake piston. Upon retraction of the brake piston, O-rings on the pin maintain the pin in the position to which it was moved by the brake piston. Upon removal of a plug at the exterior end of the bore, the axial position of the pin is measured and compared with the position of the pin when the brake was in an unworn condition to provide a determination of the amount of brake wear. This method of determining brake wear requires a measuring apparatus and a significant amount of calibration time to determine brake wear.
Heretofore, it has also been recognized that it is desirable to transmit a signal to the vehicle operator when excessive wear occurs in a friction coupling. U.S. Pat. No. 5,642,793 issued Jul. 1, 1997 to Knut T. Ljosne on an Indicator Device for Signaling that the Wear Limit has been Reached for Servo-operated Clutches discloses a clutch operating apparatus in which the clutch pedal is harder to depress when the clutch becomes excessively worn. The difficulty in operation of the clutch pedal is a matter of feel and can be interpreted differently by different operators. Thus this system of determining excessive wear of a friction coupling is viewed as being inexact.
The present invention is directed to overcoming one or more of the problems set forth above.
In one aspect of the invention a brake wear indicator device is provided for a fluid pressure operated friction coupling disposed between a machine housing and a torque-transmitting member. The extent of the movement of a fluid operated brake piston in applying the brake causes a brake wear indicator to provide a visual signal indicating that excessive wear of frictional material of the brake has occurred. In one embodiment of the invention the visual signal is the position of the end of a pin viewable through a window in the brake housing, the piston being shifted axially by the brake piston as the friction surfaces of the brake wear away. In a second embodiment of the present invention, the visual signal is a light turned on by a pressure switch activated by the pressure of the fluid operating the brake piston when the brake piston moves in a brake applying direction a predetermined distance.